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United States Patent |
6,007,960
|
Marz
,   et al.
|
December 28, 1999
|
Process for producing a colored image with reduced dot gain and colored
image obtained thereby
Abstract
A process for producing a colored image by laminating a light-sensitive
material comprising a temporary support film (i), a colored
light-sensitive layer and a heat-activable adhesive layer onto an
image-receiving material at elevated temperature and under pressure,
subjecting the light-sensitive layer to imagewise exposure and developing
by peeling off the support film, characterized in that the image-receiving
material comprises a light-sensitive compound which, on irradiation,
releases a gas which remains trapped in the image-receiving material in
the form of gas bubbles. The advantage of the process is that, on
irradiation under a halftone original, the size of the halftone dots in
the coloured image produced on such an image-receiving material is
optically reduced.
Inventors:
|
Marz; Karin (Mainz, DE);
Mohr; Dieter (Appenheim, DE);
Bodenheimer; Dieter (Aarbergen, DE);
Hilger; Manfred (Konz, DE)
|
Assignee:
|
Agfa-Gevaert (Mortsel, BE)
|
Appl. No.:
|
842791 |
Filed:
|
April 16, 1997 |
Foreign Application Priority Data
Current U.S. Class: |
430/143; 430/152; 430/253; 430/254; 430/257; 430/293 |
Intern'l Class: |
G03F 007/34; G03C 005/60 |
Field of Search: |
430/143,152,253,254,257,293
|
References Cited
U.S. Patent Documents
4093463 | Jun., 1978 | Fletcher et al. | 430/152.
|
4334006 | Jun., 1982 | Kitajima et al. | 430/143.
|
4818663 | Apr., 1989 | Powers et al. | 430/358.
|
4977070 | Dec., 1990 | Winslow | 430/152.
|
Primary Examiner: Chu; John S.
Attorney, Agent or Firm: Foley & Lardner
Parent Case Text
This application claims the benefit of U.S. Provisional Application Ser.
No. 60/021,502 filed Jul. 10, 1996.
Claims
What is claimed is:
1. A process for producing a colored image comprising laminating a
light-sensitive material comprising a temporary support film (i), a
colored light-sensitive layer and a heat-activable adhesive layer onto an
image-receiving material at elevated temperature and under pressure,
subjecting the light-sensitive layer to imagewise exposure and developing
the imagewise-exposed layer to the image, and
optionally repeating these steps with at least one further light-sensitive
film in another color,
wherein the image-receiving material comprises on a support material (ii)
at least one light-sensitive vesicular layer which has been exposed by
actinic radiation prior to said first lamination step, thereby producing a
gas by photolysis, wherein the gas remains in the light sensitive
vesicular layer and gives the layer an opaque appearance upon heating.
2. A process according to claim 1, wherein the light-sensitive layer of the
image-receiving material comprises a diazonium salt.
3. A process according to claim 2, wherein the diazonium salt is a
halogen-containing diazonium hexafluorophosphate.
4. A process according to claim 3, wherein the halogen-containing diazonium
hexafluorophosphate is 3-chloro-4-N,N'-dimethylaminobenzenediazonium
hexafluorophosphate.
5. A process according to claim 1, wherein the support material (ii) of the
image-receiving material is at least partly made of paper.
6. A process according to claim 5, wherein the support material (ii) of the
image-receiving material is a polymer-coated paper support.
7. A process according to claim 1, wherein a further, heat-activable
adhesive layer is disposed between the vesicular layer of the
image-receiving material and the thermally activable adhesive layer of the
light-sensitive color film.
8. A process according to claim 1, wherein the colored image is developed
by peeling the support film (i) and the image-receiving sheet apart.
Description
DESCRIPTION
The invention relates to a process for producing a coloured image for the
colour proofing of originals for multicolour printing, a layer material to
carry it out, and a coloured image obtained thereby.
Such a coloured image is generally produced to assist a printer in checking
and, if necessary, correcting the colour separations which will be used in
exposing the printing plates in multicolour printing. This colour-proofing
image has to be a consistent duplicate of the desired halftone or line
image. The proof should reproduce the tonal values of the colours
naturally and identically with the later printed image.
In the production of such a colour-proofing image it is customary to
produce successive primary colour images corresponding to the primary
colours of the multicolour print on an image-receiving material or
transfer them thereto.
Each primary colour image is produced by exposing and developing a
light-sensitive layer, the method of development employed being either
washing off or peeling off a support film.
Numerous materials and processes for producing such colour-proofing images
are known and described for example in the following documents: U.S. Pat.
No. 3,649,268, U.S. Pat. No. 3,642,474, U.S. Pat. No. 4,260,673, U.S. Pat.
No. 4,650,738, U.S. Pat. No. 4,656,114, U.S. Pat. No. 4,659,642, U.S. Pat.
No. 4,895,787, U.S. Pat. No. 5,049,476, EP-A 447829. In order that, in a
colour-proofing process, the tonal values of the colours visually conform
to those in the later printed image, the colour-proofing process must
allow simulation of the dot gain in printing. Dot gain is the enlargement
of the halftone dot in printing compared with the film original. There is
physical (or mechanical) dot gain and optical dot gain, depending on the
cause. Physical dot gain is an actually measurable enlargement of the
halftone dot during the printing process, which depends on various
parameters, for example the nature of the printing paper, the nature of
the printing ink, the nature of the press and also the nature of the
printing plates, etc. Optical dot gain, by contrast, has its cause in
light scattering and absorption properties (shadow effect). The actual dot
size does not change. Optical dot gain depends on the texture and opacity
of the paper and in the case of the colour-proofing image additionally on
any adhesive and release layers present. In offset printing dot gain is
depending on the parameters mentioned about 8-30% in the mid tones, i.e.
at about 40-50% coverage of the halftone. Low dot gains are preferred for
high quality prints because of the higher sharpness of image.
The colour-proofing image production materials described in the cited
references consist of a plurality of layers on temporary support films.
Colourless release and/or adhesive layers are the cause in the
ready-produced colour-proofing image of an optical dot gain which
generally amounts to about 20-25%. Within certain limits, the dot gain in
the colour-proofing image can be controlled by the thickness of the
adhesive or release layers, as described for example in U.S. Pat. No.
4,262,071 and EP-A 339860. The possibility of reducing dot gain by means
of thin adhesive layers, however, is restricted by processing
difficulties, which necessitate an increase in the lamination temperature
or a reduction in the lamination speed. A further possible way of reducing
dot gain is to add white pigments, for example titanium dioxide, to the
adhesive layer of the colour films or to the image-receiving material. If
the titanium dioxide is added to the adhesive layer of the colour films,
only the colour film for the first primary colour image can in each case
be provided with such a TiO.sub.2 -containing adhesive layer, since, in
the following layers, the white pigment would affect the colour. Hence the
sequence of colours in the construction of the image is disadvantageously
predetermined and, what is more, only a small reduction in the dot gain is
achieved. Such a material is described in EP-A 420675.
Preference is given to processes where dot gain can be controlled without
changing the colour film material, for example by adding TiO.sub.2 to the
image-receiving material, described in EP-A 305599 and EP-A 625224, for
example. Instead of titanium dioxide it is also possible to use barium
sulphate, calcium carbonate or titania-containing pearl lustre pigments
described in EP-A 186902. The white pigment may also be applied to the
image-receiving material as an additional primer layer, described in EP-A
639736. To ensure adequate adhesion to the receiving sheet, the primer
layer has in this instance to be constructed of two layers--an adhesive
layer and a layer containing the white pigment.
As a further way of reducing dot gain by means of a specific
image-receiving material the literature mentions air-filled films,
including in combination with titanium dioxide (EP-A 186902). The
complicated manufacture of these films is described by Mathews et al. in
U.S. Pat. No. 3,944,699. It takes the form of extrusion of a mixture of
polyester and polyethylene or polypropylene with sub-sequent biaxial
drawing and tempering. The polymers have to be mixed in the granulated
state prior to extrusion. The coextrusion of the melts does not result in
air-filled films. Mathews et al. describe the use of the films thus
manufactured as substrates for photographic purposes. There is no mention
of an influence on optical dot gain when used as a substrate for halftone
images. Apart from their complicated manufacture, the disadvantage of
these films is that there is no similarity with printing paper.
The present invention describes a process using as the image-receiving
material for a colour-proofing image a support consisting of film or paper
coated with a light-sensitive layer in which gas bubbles form on
irradiation. The photolytically produced gas remains in the layer and
gives it an opaque appearance on heating. The heating necessary to develop
the gas bubbles can preferably also take place simultaneously with the
lamination of the 1st primary colour image. The order of the primary
colour images is freely choosable. Materials according to the invention,
known as vesicular film, are described for example in EP 038016. If the
vesicular layer is applied to a paper support, the colour-proofing image
obtained is particularly similar to the print outcome to be simulated.
The preferred embodiment of the process of the invention comprises first
preparing a layer material consisting of a temporary support (1) and a
vesicular layer (2). The temporary support (1) preferably consists of
polymer or polymer-coated specialty paper. The composition of vesicular
layer (2) is described for example in EP-B 038016, FR-A 2 304 944, U.S.
Pat. No. 3,622,336 and DE-A 2 438 157. It preferably includes a binder
having a glass transition temperature of max. 130.degree. C., so that the
development temperature is max. 150.degree. C.
Such preferred binders include for example copolymers of methacrylo-nitrile
and vinylidene chloride. The light-sensitive compounds used for the
vesicular layer (2) are preferably diazonium compounds which evolve
nitrogen on irradiation. In this connection, particular preference is
given to diazonium salts which form a vesicular layer on exposure and
development. However, it is also possible to use any other compound which
forms a gas by photolysis.
The vesicular layer (2) on the temporary support (1) is uniformly exposed
to UV light until the light-sensitive compound has completely decomposed.
When diazonium compounds are used, the decomposition is evidenced by the
disappearance of the yellow colouring. When Ga-doped UV light sources
having a power of 5 kW are used together with diazonium salts, for
example, just a few seconds (20 s) are sufficient for complete
decomposition. Longer exposure times are uncritical.
The exposed vesicular layer (2) has laminated onto it a colour-proofing
film (F) under heat and pressure. The colour-proofing films preferred for
the process of the invention consist of a temporary support (3), a
light-sensitive colour layer (4) and an adhesive layer (5). Such materials
are described for example in EP-A 352 055, U.S. Pat. No. 4,895,787, U.S.
Pat. No. 5,049,476 and EP-A 525 624. The colour-proofing film is laminated
onto the vesicular layer (2) with the adhesive layer (5). The lamination
temperature is preferably sufficiently high for the vesicular layer to be
thermally developed in the course of this lamination process and at the
same time for the adhesive layer (5) to soften, to form a composite of
colour-proofing film and vesicular layer. Typically the lamination
temperature is 120.degree. C. This method is preferred since it does not
require an additional operation to develop the vesicular layer. However,
the vesicular layer can also be thermally developed in some other way, for
example in an oven, before the lamination of the first colour-proofing
film. The light-sensitive layer (4) of the colour-proofing film is
subjected to imagewise exposure through the support film (3) underneath a
colour separation film before or preferably after lamination and developed
after lamination onto the vesicular layer (2). This development must not
attack the vesicular layer, which is why particular preference is given to
dry-developable, peel-apart colour-proofing materials, which are developed
by peeling off the temporary support film (3) after exposure. The
colour-proofing materials described in EP-A-352 055, U.S. Pat. No.
5,049,476 and EP-A 525 624 are developed in this way.
After the development of the first primary colour image, the lamination,
exposure and development of the second primary colour image but also of
the subsequent primary colour images takes place until a complete
colour-proofing image is obtained on the vesicular layer (2). This
colour-proofing image has the advantage of lower dot gain over a
colour-proofing image produced directly on a polymer-coated paper as
support (1).
EXAMPLES
The examples which follow illustrate the invention. The dot gain (S.sub.2
-S.sub.1) is calculated using test films having calibrated degrees of
coverage (S.sub.1) as exposure mask, according to the equation of
Murray-Davies:
##EQU1##
S.sub.2 : coverage of halftone field in proof S.sub.1 : coverage of
halftone field in film original
D.sub.S : colour density in halftone field
D.sub.V : colour density in full tone
The densities D.sub.s and D.sub.v are measured with a densitometer.
Example 1: Preparation of a vesicular film
A solution having the following composition is cast onto a biaxially
oriented, 150 .mu.m thick film of polyethylene
______________________________________
Constituents Parts by weight
______________________________________
Copolymer of methacrylonitrile and
12.8
vinylidene chloride (comonomer ratio 70:30)
Copolymer of methacrylonitrile and 3.2
vinylidene chloride (comonomer ratio 20:80;
Saran .RTM. F310, Dow Chemical)
4-Morpholino-2,5-diisopropoxybenzene- 0.8
diazonium tetrafluoroborate
Silicone oil (as flow-control agent) 0.05
2-Butanone 80.0
______________________________________
The layer is dried initially at 70.degree. C. for 60 s and then at
130.degree. C. for 30 s. The weight of the dried layer is 8 g/m.sup.2. The
film obtained has a yellow colour.
Example 2: Preparation of colour-proofing films for producing a
colour-proofing image according to the invention
Four light-sensitive colour-proofing films are prepared in the process
colours of multicolour printing (cyan, magenta, yellow and black) by first
applying coating solutions of the following compositions in each case to a
50 .mu.m thick, biaxially oriented, heat-set and adhesion-promoted
polyethylene terephthalate film and drying. The drying takes place at
70.degree. C. for 2 min. The layer weights are 0.4-0.8 g/m.sup.2 ; they
are selected so that the densities of a standard multicolour print are
later achieved in the ready-produced colour-proofing image.
______________________________________
Parts by weight
Constituents Cyan Magenta Yellow Black
______________________________________
1. Hostaperm Blue .RTM.B2G
7
(C.I. 74160)
2. Permanent Yellow GR 7
(C.I. 21100)
3. Permanent Carmine 12
FBB (C.I. 12485)
4. Carbon Black 11
(Printex .RTM. 25)
5. Polyvinyl formal 6 18 13 9
(Formvar .RTM. 12/85,
Monsanto)
6. 2,3-Bis(4-methoxy- 4 4 4 4
phenyl)quinoxaline
7. Dipentaerythritol 8 8 12 12
pentaacrylate
8. .gamma.-Butyrolactone 44 89 65 90
9. Tetrahydrofuran 200 200 200 200
10. 1-Methoxy-2- 444 489 465 490
propanol
______________________________________
Pigments 1.-4. are ball-milled with part of the binder (5.) and of the
solvent (8.) before their addition to the respective solution.
An adhesive solution of the following composition is applied to the dried,
light-sensitive colour layers and dried at 100.degree. C. for 2 min. The
dry adhesive layers each have a weight of 7 g/m.sup.2.
______________________________________
Constituents Parts by weight
______________________________________
Copolymer of vinyl acetate and
50.0
crotonic acid (comonomer ratio
95:5; Mowilith .RTM.CT5, Hoechst AG)
Polyvinyl methyl ether (Lutanol .RTM. 1.0
M40, BASF)
Water 253.3
Ethanol 24.0
Ammonia solution (25% strength) 5.0
______________________________________
Example 3: Preparation of a colour-proofing image on a vesicular film
The vesicular film of Example 1 is exposed for 20 s in a contact copying
frame (5 kW, Ga-doped burner). After exposure, the film no longer shows
the typical intensive yellow colouring, but is still transparent. The cyan
film of Example 2 is laminated with the adhesive-layer side onto the layer
side of the exposed vesicular film at 120.degree. C. and under pressure.
The vesicular film becomes opaquely white as a result. The cyan film of
the laminate is subjected to imagewise exposure under a colour separation
film (60 lines per cm screen) through its 50 .mu.m thick support film. The
exposure time is chosen so that the tonal value range is 3-98%. After
exposure, this support film is peeled off the colour-proofing film. The
unexposed areas with the entire adhesive layer remain on the vesicular
layer, while the exposed areas of the colour layer are peeled off together
with the support film. The steps of
lamination of the colour-proofing film
exposure under the respective colour separation film and
peeling the support film off the colour-proofing film are repeated for the
colours magenta, yellow and black. To conclude, a matte or bright
protective layer can be applied.
The colour densities are measured with a commercially available incident
light densitometer (D186 from Gretag). A plurality of layers of white
paper are used as measuring background. The colour densities can be used
to calculate the dot gain according to the equation of Murray-Davies (see
page 6). The tonal value range is checked visually using an eye glass. The
results are shown in Table 1.
TABLE 1
______________________________________
Coverage Dot gain Dot gain Dot gain Dot gain
Film (S.sub.1) cyan magenta yellow black
______________________________________
40% 19 21 17 21
80% 10 13 11 12
______________________________________
Example 4 (Comparative example): Colour-proofing image on a support
material without vesicular layer
The colour-proofing films of Example 2 are laminated in succession in the
same order as in Example 3 onto a polymer-coated specialty paper
(Ozasol.RTM. TF01) instead of onto a vesicular film, exposed and
developed. Exposure is carried out in such a way that the tonal value
range of every colour is identical in Example 3 and Example 4; only then
are the dot gains comparable. Again the dot gains of the primary colours
are determined in the ready-produced colour-proofing image. The results
are shown in Table 2:
TABLE 2
______________________________________
Coverage Dot gain Dot gain Dot gain Dot gain
Film (S.sub.1) cyan magenta yellow black
______________________________________
40% 22 24 22 24
80% 12 14 12 13
______________________________________
The comparison with the values of Table 1 shows a reduction in dot gain in
Example 3 by 3-5% at a coverage of 40% and by 1-2% at a coverage of 80% in
the film original.
Example 5: Preparation of a paper support with vesicular layer
A solution of the following composition is applied to the polymer-coated
specialty paper of Example 4 (Ozasol.RTM. TF01) and dried. Drying is 1 min
at 70.degree. C. The layer weight is about 10 g/m.sup.2.
______________________________________
Constituents Parts by weight
______________________________________
Copolymer of methacrylonitrile and
18.4
vinylidene chloride
(comonomer ratio 70:30)
Copolymer of methacrylonitrile and 0.8
vinylidene chloride
(comonomer ratio 20:80; Saran .RTM. F310,
Dow Chemical)
3-Chloro-4-N,N'-dimethylaminobenzene- 0.76
diazonium hexafluorophosphate
Silicone oil (as flow-control agent) 0.03
Citric acid 0.13
2-Butanone 20.0
______________________________________
The support obtained has a yellow colour on the vesicular layer side. After
exposure, which is carried out in the manner described in Example 3, the
yellow colouring disappears. This support can either be used directly for
preparing a colour-proofing image or else be first provided with an
additional adhesive layer to ensure better adhesion of the image. To this
end, a layer of the following composition is applied to a further
temporary support film consisting of biaxially oriented and heat-set
polyethylene terephthalate without adhesion promotion and dried. The
weight of the dried layer is 20 g/m.sup.2.
______________________________________
Constituents Parts by weight
______________________________________
Polyvinyl acetate (Mowilith .RTM. 30, Hoechst)
25
2-Butanone 75
______________________________________
This adhesive-layer film is laminated with the layer side face down onto
the specialty paper coated with the exposed vesicular layer. The support
film of the adhesive-layer film is peeled off; the additional adhesive
layer remains on the vesicular layer, which was thermally developed at the
same time as the lamination of the additional adhesive-layer film.
Example 6: Preparation of a colour-proofing image on a paper support with
vesicular layer
A colour-proofing image is prepared on the specialty paper of Example 5,
provided with an exposed vesicular layer and additional adhesive layer,
analogously to Examples 3 and 4 by lamination, exposure and peeling off of
the four colour-proofing films, and the dot gain is measured in the
ready-produced proof. The values obtained are compared with those obtained
in the case of a proof on TF01 without vesicular layer but (for reasons of
comparability) with the additional adhesive layer of Example 5. The
results are shown in Table 3.
TABLE 3
______________________________________
Cover-
age Dot Dot Dot Dot
Film gain gain gain gain
Support (S.sub.1) cyan magenta yellow black
______________________________________
TF01 + vesicular +
40% 20 17 19 27
adhesive layer
TF01 + vesicular + 80% 11 12 12 14
adhesive layer
TF01 + adhesive 40% 26 24 23 28
layer
TF01 + adhesive 80% 12 13 12 14
layer
______________________________________
The comparison of the values shows a reduction in the dot gain due to the
vesicular layer by 1-7% at a coverage of 40% and by 0-1% at a coverage of
80% in the film original. The effect is distinctly less with the fourth
primary colour image (black) than with the first two primary colour images
(cyan and magenta). The additional adhesive layer distinctly increases the
dot gains in comparison with Example 4 without the action of the vesicular
layer. The dot gain increase due to additional adhesive layers is known
(see page 1 et seq.). With a vesicular layer it is thus possible to
utilize the advantages of an additional adhesive layer (for example
reduction in dust inclusions during lamination) without the simultaneous
disadvantage of a dot gain increase. By using a polymer-coated paper as
support, the proof obtained in this example is more similar to the final
print result than a colour-proofing image obtained according to Example 3
on a vesicular film.
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